A resonant tunneling diode (RTD) is an example of a terahertz oscillator of a current injection type that generates an electromagnetic wave in a frequency range of 30 GHz to 30 THz (referred to as terahertz wave in this description). The RTD is capable of generating the terahertz wave at a room temperature using an electromagnetic wave gain based on electron transition between subbands in a semiconductor quantum well structure.
Patent Literature 1 (Japanese Patent Laid-Open No. 2007-124250) discloses a terahertz oscillator formed by accumulating an active layer composed of a double-barrier RTD and a planar slot antenna resonator on a semiconductor substrate. The oscillator generates an electromagnetic wave by stimulated emission in a range of negative differential resistance in a current-voltage (I-V) characteristics of the RTD.
The terahertz oscillators including the RTD are well known that parasitic oscillations in bias circuit arise. The parasitic oscillation is an oscillation at a frequency other than the desired resonant frequency, which is determined by the structure of the resonator, in a terahertz frequency band. Therefore, the parasitic oscillation causes a reduction in an oscillation output at the desired resonant frequency.
Accordingly, Non Patent Literature 1 (IEEE Microwave and Guided Wave Letters, Vol. 5, No. 7, July 1995, pp 219-221) discloses a method of arranging a stabilizing circuit between a bias power supply and an RTD. The stabilizing circuit includes a resistor and a capacitor arranged in parallel to the RTD, and serves to reduce the impedance of a resonant circuit at all of the frequencies other than the resonant frequency. The stabilizing circuit is positioned within lambda/4 (lambda is a wavelength corresponding to the desired resonant frequency in the terahertz frequency range) from the RTD.
Patent Literature 1 also discloses a stabilizing circuit including a parallel resistor having the structure of a bismuth resistor and parallel capacitors having a metal-insulator-metal (MIM) layered structure. These components are integrated on the same substrate together with the RTD and the slot antenna resonator to generate an oscillation in a terahertz frequency range.
Patent Literature 2 (Japanese Patent Laid-Open No. 2006-101495) discloses a terahertz oscillator in which an RTD and a microstrip resonator (resonator including two conductors and a dielectric interposed therebetween) are integrated on the same substrate.